Addition of severely-hindered amine salts and/or aminoacids to non-hindered amine solutions for the absorption of H2 S

Abstract

A new alkaline absorbent solution containing the additive of a severely-hindered amine salt and/or a severely-hindered aminoacid to a non-hindered amine such as N-methyldiethanolamine (MDEA) is provided. A process for the removal of H2S from fluid mixtures using this absorbent solution to produce a very low level of H2S in the treated fluid is also provided. The process is also suitable for the selective removal of H2S from fluid mixtures comprising H2S and CO2. Use of the above absorbent solution leads to higher selectivity for H2S than observed when MDEA is used alone without the additives.

What is claimed is: 
     
       1. An absorbent composition comprising: (1) MDEA and, optionally, at least one other non-hindered amino compound, and   (2) an additive of (a) a severely hindered aminoacid having a cumulative -E s  value greater than 1.75, said aminoacid and non-hindered amino compound being present in said absorbent composition in a mole ratio of said aminoacid to said non-hindered hindered amino compound of about 0.01:1 to 4:1,   (b) an amine salt, said amine salt being the reaction product of an amine selected from the group consisting of severely hindered amino compounds having a cumulative -E s  value greater than 1.75, and a component selected from the group consisting of an acid having at least one pKa of not more than about 7, a decomposable salt of an acid having at least one pKa of not more than about 7, a compound capable of forming an acid having a pKa of not more than about 7 and mixtures thereof, said amine salt and said non-hindered amino compound being present in said absorbent composition in a mole ratio of said amine salt to said non-hindered amino compound of about 0.2:1 to 4:1.     
     
     
       2. The absorbent composition of claim 1 wherein said absorbent composition additionally comprises a liquid selected from the group consisting of water, an organic solvent and mixtures thereof. 
     
     
       3. The absorbent composition of claim 1 wherein said severely hindered amino compound of said amine salt is selected from the group consisting of a secondary amino ether alcohol, a di-secondary amino ether, and mixtures thereof. 
     
     
       4. The absorbent composition of claim 1 wherein said compound reacted with said severely hindered amino compound is selected from the group consisting of sulfuric acid, phosphoric acid, phosphorous acid, pyrophosphoric acid, sulfurous acid, and mixtures thereof. 
     
     
       5. The absorbent composition of claim 1 wherein said component reacted with said severely hindered amino compound is selected from the group consisting of ammonium sulfate, ammonium sulfite, sulfur dioxide, ammonium phosphate and mixtures thereof. 
     
     
       6. The absorbent composition of claim 1 which includes said aminoacid wherein said mole ratio of said aminoacid to said non-hindered amino compound ranges from about 0.2:1 to 1:1. 
     
     
       7. The absorbent composition of claim 1 which includes said aminoacid wherein said mole ratio of said aminoacid to said non-hindered amino compound ranges from about 0.3:1 to 1:1. 
     
     
       8. The absorbent composition of claim 1 wherein said absorbent composition comprises water and wherein said amine salt is a non-volatile water soluble amine salt. 
     
     
       9. The absorbent composition of claim 1 wherein said non-hindered amino compound is solely N-methyldiethanolamine (MDEA) and said amine salt is ethoxy-ethanol-tertiarybutylamine (EETB) sulfate. 
     
     
       10. The absorbent composition to claim 1 wherein said absorbent composition comprises from about 5 to 70 wt. % of said non-hindered amino compound from about 5 to 50 weight percent of said amine salt and/or aminoacid calculated as amine, and the balance being water. 
     
     
       11. The absorbent composition of claim 1 wherein said amino acid is selected from the group consisting of N-tertiarybutylalanine, N-tertiarybutylglycine, and mixtures thereof. 
     
     
       12. The absorbent composition of claim 1 which includes said amine salt wherein said mole ratio of said amine salt to said non-hindered amino compound ranges from about 0.2:1 to 1:1. 
     
     
       13. The absorbent composition of claim 1 which includes said amine salt wherein said mole ratio of said amine salt to said non-hindered amino compound ranges from about 0.3:1 to 1:1.